Which of the following is NOT a secondary lymphoid organ?

Correct Answer: A

Rationale: The correct answer is A: Bone marrow. Secondary lymphoid organs are where immune responses are initiated. Bone marrow is a primary lymphoid organ where immune cells mature, not where immune responses are initiated like in secondary lymphoid organs. The spleen, lymph nodes, and mucosal immune system are all secondary lymphoid organs where immune responses occur.

Correct Answer: B

Rationale: The correct answer is B: Recognition, ingestion, and digestion. Firstly, recognition is essential for phagocytes to identify and bind to the target. Next, ingestion involves engulfing the target into a phagosome. Finally, digestion occurs within the phagolysosome, where enzymes break down the target. Choices A, C, and D are incorrect because they do not accurately represent the sequential key steps of phagocytosis.

Correct Answer: D

Rationale: The correct answer is D. Innate immunity does not involve producing antigen-specific antibodies. This is because innate immunity is the first line of defense against pathogens and does not have the ability to produce antibodies that target specific antigens. Instead, innate immunity works through mechanisms like phagocytosis and killing infected cells to eliminate pathogens. Choices A, B, and C are functions of innate immunity. A - Killing virally infected cells is a common function of innate immunity. B - Phagocytosis is the process by which immune cells engulf and destroy pathogens, a key function of innate immunity. C - Activating adaptive immunity is also a role of innate immunity, as it helps initiate the adaptive immune response for a more targeted defense.

Correct Answer: C

Rationale: Rationale: 1. Deficiencies in the classical pathway lead to impaired clearance of immune complexes, hence contributing to SLE. 2. This pathway plays a crucial role in removing self-antigens and maintaining immune tolerance. 3. Increased cancer risk (A) is not directly linked to classical pathway deficiencies. 4. Resistance to bacterial infections (B) is more associated with deficiencies in the alternative pathway. 5. Overactivation of adaptive immunity (D) is not a direct consequence of classical pathway deficiencies.

Correct Answer: B

Rationale: The correct answer is B: C3b acts as an opsonin to enhance phagocytosis. C3b binds to pathogens and enhances their recognition by phagocytic cells, facilitating their engulfment and destruction. This process is crucial for efficient immune responses. A, MAC formation, is initiated by the membrane attack complex, not C3b. C, inflammation, is triggered by various mediators such as histamine and cytokines, not C3b. D, neutralizing cytokines, is not a function of C3b; cytokines are regulatory proteins involved in immune responses.